1. Field of the Invention
The present invention relates to a positioning device for a motor bearing and, more particularly, to a positioning device capable of reliably positioning a motor bearing in a predetermined position.
2. Description of the Related Art
FIG. 1 shows a conventional motor including a rotor 91, a stator 92, and a base 93. The rotor 91 includes a shaft 911. The base 93 includes a shaft tube 931 around which the stator 92 is mounted. An abrasion-resistant plate 932, a restraining member 933, a bearing 934, and a washer 935 are mounted in the shaft tube 931. A positioning member 936 is mounted on a top end of the shaft tube 931 to prevent disengagement of the elements received in the shaft tube 931. In assembly, the shaft 911 of the rotor 91 is extended through the positioning member 936, the washer 935, the bearing 934, and the restraining member 933. The restraining member 933 extends into an annular groove defined in a neck portion of the shaft 911, preventing disengagement of the shaft 911. The stator 92 can drive the rotor 91 to rotate. The bearing 934 presses against the restraining member 933 and is retained in a predetermined position in the shaft tube 931. An example of such a motor is disclosed in Taiwan Publication No. 200822497. However, positioning of the bearing 934 in the shaft tube 931 in an axial direction is not reliable. Specifically, in a case that the bearing 934 is too low in the axial direction, the restraining member 933, if made from a high-molecular material, is liable to be damaged by the downwardly pressing force imparted from the bearing 934 (FIG. 2). On the other hand, with reference to FIG. 3, a gap exists between the restraining member 933 and the bearing 934 when the bearing 934 is too high in the axial direction, such that the bearing 934 can not be positioned. Thus, the restraining member 933 and the bearing 934 will move up and down in the axial direction during rotation of the shaft 911 and generate noise.